[(2R,3S,4S,5S)-5-[[tert-butyl(diphenyl)silyl]oxymethyl]-2-(2,4-dioxopyrimidin-1-yl)-4-methyl-5-(methylsulfonyloxymethyl)oxolan-3-yl] trifluoromethanesulfonate;1-[(1R,3R,4R,7S)-1-[[tert-butyl(diphenyl)silyl]oxymethyl]-7-hydroxy-5-(2-methoxyethoxy)-2-oxa-5-azabicyclo[2.2.1]heptan-3-yl]pyrimidine-2,4-dione;1-[(1R,3R,4R,7S)-1-[[tert-butyl(diphenyl)silyl]oxymethyl]-5-(2-methoxyethoxy)-7-methyl-2-oxa-5-azabicyclo[2.2.1]heptan-3-yl]pyrimidine-2,4-dione